1/4 c. BUTTER, softened Combine flour, sugar, lemon peel and vanilla. Make well in Center. Blend in yolk and butter. Mix with fingers till Smooth. Pat half of dough onto pan bottom. Bake 6-8 min At 400-degrees. Pat rest of dough 2 inches up pan sides. Increase heat to 450-degrees and place a pan of water in Bottom of the oven. FILLING